1. Field of the Invention
The present invention relates to a top emission type organic electroluminescence (EL) device.
2. Background of the Related Art
The organic EL device has advantages in that a low voltage operation is possible and power consumption is small. FIG. 1 illustrates a section of a related art top emission type organic EL device.
Referring to FIG. 1, an anode 2 is formed on a transparent substrate 1. The anode 2 is formed of ITO (indium tin oxide), mostly. A hole injecting layer (HIL) 3 is formed on the anode 2. The HIL 3 is formed of approx. 10–30 nm thick CuPc (copper phthalocyanine).
Then, a hole transport layer (HTL) 4 is formed on the HIL 3. The HTL 4 is formed of approx. 30–60 nm thick N,N′-diphenyl-N,N′bis(3-methylphenyl)-(1-1′-biphenyl)4,4′-diamine (TPD), or 4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl(NPD).
Then, an organic emitting layer 5 is formed on the HTL 4, and an electron transport layer (ETL) 6 and an electron injecting layer (EIL) 7 are formed on the organic emitting layer 5 in succession. The electron injecting layer 7 is formed of approx. 5 Å thick LiF or Li2O, or approx. 200 Å thick alkali metal or alkali earth metal, such as Li, CA, Mg, Sm and the like.
Then, a cathode 8 is formed on the electron injecting layer 7. The cathode 8 is formed of approx. 1000 Å thick ITO, or IZO.
Thus, since the top emission type organic EL device is required that a light emitted from the organic emitting layer transmits toward the cathode, the cathode is formed of transparent material, such as ITO, or IZO.
An oxide film of ITO or IZO is very sensitive to a temperature. Therefore, for better electrooptic characteristics of the oxide film, it is required to maintain a temperature of the substrate in a range of approx. 200–300° C. in formation of the cathode. However, because an organic material, like the organic emitting layer, is susceptible to a high temperature, it is required to maintain a temperature of the substrate in a range of 100° C. in formation of the cathode, which results in poor electrooptic characteristics of the cathode of an oxide film.